Understanding tree architecture, form and function in the tropics

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The basic shape and branching structure of a tree can be distinctive and characteristic, yet there exists no consistent dataset quantifying how tree form varies across species and how it is related to other functional traits of a tree. Understanding the variation in structure and form of trees is important in order to link tree physiology to tree performance, scale fluxes of water and carbon within and among trees, and understand constraints on tree growth and mortality. These topics hold great importance in the field of ecosystem science, especially in light of current and future changes to climate. It is surprising, therefore, that tree structure and form are currently neglected areas of study. There are two primary reasons for this neglect: 1) it is difficult and time-consuming to quantify tree structure in-situ and 2) there is a lack of theory that explicitly links tree form parameters with physiological function.Recent developments in technology and theory now enable us to overcome these limitations. In this proposal we aim to use new ground-based 3D terrestrial laser scanning technologies (TLS) in combination with recently developed theoretical frameworks to measure and compare tree architecture. We focus on the tropics, since (i) they host the vast majority of broadleaf tree diversity and play a disproportionate role in global and regional carbon and water fluxes, and (ii) the high species diversity of tropical forests (typically 100-250 tree species per hectare) means we can sample a large number of species under almost identical climate and soil conditions, making it more likely to detect overall tendencies in tree form response to environment that are not dominated by the peculiarity of a particular species. Specifically, we will employ TLS to collect highly-detailed 3D structural information from mature rainforest trees spanning contrasting environments ranging from cloud forests to wet rainforests to dry savanna, and contrasting biogeographical histories from the cloud forests of the Andes through legume-dominated forests of Amazonia and Africa, through the dipterocarp-dominated tall forests of Borneo, to the ancient rainforest flora of Australia. All field sites are locations where we have already collected information of the leaf and wood traits of a number of tropical trees. We plan to achieve three goals: i) definition of quantitative classes of tree form using advanced imaging and computational techniques, ii) development of an understanding of the degree of covariance between tree form and tree leaf and wood functional traits, and the degree of phylogenetic constraint and plasticity in tree form, iii) testing and refinement of metabolic-scaling based approaches to scaling fluxes and productivity of tropical tree communities. Over the course of three years our team will:1) Create a database of branch- and canopy-level trait data collected from our field campaigns. 2) Use variation in branching architecture and canopy structure traits to define a suite of branching and canopy traits that allow for the classification of tree form.3) Assess the scaling of tree form traits within trees and integrate the scaling of tree-form into a mechanistic plant scaling framework.4) Explore the link between tree-form traits and leaf and wood traits to determine a whole-tree integrated economics spectrum. In doing so, we hope to acquire a mechanistic understanding of the relationship between tree form, function, phylogeny and environment over a large spatial scale. We expect to find that behind the dazzling variety of shapes and forms found in trees hides a remarkably similar architecture based on fundamental, shared principles.